SWG Output for Attached Spa

[johig]

I have an attached (raised) spa with a spillover to the main pool. All equipment is shared between the pool and spa, with a single variable speed pump. When the pool was completed and set up, the SWG was set to run at 25% with the pump in "pool" mode but only 1% with the pump in "spa" mode.
- Is there a good reason for having the output so low for the spa?
- Should I raise it to something higher?
- I can imagine it makes sense for SWG output to be a bit lower for the spa than the pool given the much smaller volume of the spa, but is 1% too low?
- Some days the spa is very popular and the equipment spends a lot of time in spa mode, so I also worry that the FC in the whole system will drop too low without additional SWG output.

Overall, I'm not having any problems keeping FC levels within range by tweaking the SWG output and pump run time in pool mode, but I have left the spa mode SWG output unchanged at 1%. I'm just wondering if there is a better approach to chlorinating the spa during usage. As always, any insight is much appreciated!

 

[Hootz]

Since there is only a small percent of water in your spa compared to the pool volume it makes sense that your swg percentage needs to be lower in spa mode. The amount of water in your spa should be reasonably easy to calculate. Using pool math, add your pool volume and swg percentage to see how much fc you are adding. Then use your spa water volume and desired fc to determine swg percentage.

 

[mguzzy]

How often does the pool water recirculate through the spa? When that happens that will mix the chem between two volumes of water anyway.

 

[Jimrahbe]

J,

If you had it in the spa mode for hours the FC could get very high... In pool/spas that do not have automation they often do not even plumb the SWCG to add chlorine to the spa at all.. The spa gets its chlorine for the spa water spilling over into pool.

Thanks,

Jim R.

 

[johig]

Since there is only a small percent of water in your spa compared to the pool volume it makes sense that your swg percentage needs to be lower in spa mode. The amount of water in your spa should be reasonably easy to calculate. Using pool math, add your pool volume and swg percentage to see how much fc you are adding. Then use your spa water volume and desired fc to determine swg percentage.

Great idea. I think I have most of that data already in Pool Math, just need to add the spa volume. I'm pretty sure I calculated it previously and can dig it up. If not, like you said, pretty easy (especially as it is a square). Thanks!

 

[johig]

J,

If you had it in the spa mode for hours the FC could get very high... In pool/spas that do not have automation they often do not even plumb the SWCG to add chlorine to the spa at all.. The spa gets its chlorine for the spa water spilling over into pool.

Thanks,

Jim R.

Great input. This is the type of safety concern I was worried about before jumping into any changes. Thank you!

 

[johig]

How often does the pool water recirculate through the spa? When that happens that will mix the chem between two volumes of water anyway.

That is a great question, and I guess maybe the most important thing I don't actually know for sure. My sense is that the percentage exchanged during spa mode is very low. Probably limited to whatever goes over the spillway. That would make practical sense to avoid losing any more heat than is necessary. It would also suggest that chlorine could build up over time if I'm not careful. Thanks for the insight!

 

[ajw22]

Before you get too worked up over it turn on your spa and do a FC test on the spa water. Then come back an hour or two later and do a FC test. See how much the FC changed per hour.

Calculate how many hours it will take for your spa FC to get over the SLAM FC level for your CYA - FC/CYA Levels

Then decide if the spa gets used for that long or just make that time the limit before you turn the spillover on and exchange the spa water and start over.

 

[johig]

Before you get too worked up over it turn on your spa and do a FC test on the spa water. Then come back an hour or two later and do a FC test. See how much the FC changed per hour.

Calculate how many hours it will take for your spa FC to get over the SLAM FC level for your CYA - FC/CYA Levels

Then decide if the spa gets used for that long or just make that time the limit before you turn the spillover on and exchange the spa water and start over.

Thanks Allen, good idea. I'm thinking it might even be the opposite at 1% output. A gradual drop in FC drops over time? No need to guess, I suppose. Just try the test!